Control system for hoist motors



March 25, 1952 D. L. PETTIT CONTROL SYSTEM FOR HOIST MOTORS 4 Sheets-Sheet l Filed D60. 17, 1948 IOB ARMQTURE 8 kl/n rL/ MASTER CONTROLLER R 5|||1L|||x||li||| lxlllll llllllx l I I l llxlilx l W 3|||||u|||lx||| s l I ||x l l l Il: l l Illlv I 1 l i L Z ||x||||li||| IL ||x n l r1: 1 l I1 |-.|l|x|||!l||.'|||| ||||LT||| xllllllx l 1 1 x l l I A l l' l 4 5 7 8 9 wwfgz @E L: EL d: n H o 2 -Iii l .IH MNH .u M [.INMMNNHI. ||.|||l www .MHHIINH l.- we: m 5 .l1 l- I. H ro |ll I I I l l l l I l s l l l l l l- 1 ,u c 1 1 c l EVOII w w .sys l.

March 25, 1952 D. L. PETTl-r 2,590,453

CONTROL SYSTEM FOR HOIST MOTORS Filed Dec. 17, 1948 4 Sheets-Sheet 2 NQ' 1 LowEra j 3 l?? /sr Ll LZ NQ 2 LOWER 21g/zb. 4.

March 25, 1952 D, L, PET-HT 2,590,453

CONTROL SYSTEM FOR HOIST MOTORS Filed D60. 17, 1948 4 Sheets-Sheet i5 March 25, 1952 D. L. PE'rTl-r 2,590,453

CONTROL SYSTEM FOR ROTsT MOTORS Filed DSO. 17, 1948 4 Sheets-Sheet 4 MASTER T52-16. @o1 2 CONTROLLER 43B 3l 43B N9A '1 LOWER N9' 2 LOWE? 54H 4ms 44,5 54 45B 4 44E 3,8 49.! @LLL if; LL2

jyl. 159.19. 3 NQ 3 LOWER 43 3l NQ@ LowER 43 Tg OEB T@ OEB K32 50.` fsa 50% l E 54 4 1 4@ 54m- 4g@ may Patented Mar. 25, 1952 CONTROL SYSTEM FOR HOIST MOTORS Dorn L. Pettit, Milwaukee, Wis., assignor to Square D Company, Milwaukee, Wis., a corporation of Wisconsin Application December 17, 1948, Serial No. 65,873

(Cl. S18-2,74)

14 Claims.

This invention relates to motor control systems and refers particularly to the control of D. C. series type hoist motors. In such control systems it is customary to employ dynamic braking in conjunction with a so-called series brake which sets automatically when the controller is brought to its off position and also in the event of voltage or current failure. Hoist motor controls of this type heretofore available have been relatively costly, both from the standpoint of initial cost and upkeep, due to the large resistor bank and numerous contactors or switches they required.

It is, therefore, one of the objects of this invention to provide an improved control system for hoist motors and the like which uses fewer contactors and resistors Without sacrificing reliability, safety or accuracy of control.

Another' object of this invention is to provide increased safety against the probability of uncontrolled lowering under load, through the incorporation of a novel dynamic braking circuit characterized by the provision of parallel resistor circuits through which the armature is connected across the iield of the motor. These multiple dynamic braking loops afford greater assurance of effective dynamic brakingunder all circumstances.

Since the resistors used in controls of this type are generally quite large and expensive it is desirable to reduce the size of the resistor bank as much as possible and to this end it is another object of this invention to provide a circuit which incorporates maximum reuse of resistors, i. e., wherein many of the same resistors are used during both hoisting and lowering.

Another important object of this invention is to provide a control system of the character described wherein the currents broken by the contactors as they open to effect speed changes are relatively light.

Another purpose of this invention is to provide a hoist control system wherein the increments of speed change are closely spaced at the lower speeds and relatively widely spaced at high speed Aso that the result resembles geometric speed progression. As will be apparent to those skilled in the art the smaller increments of speed change at low speeds affords the operator better control over the load.

Still another object of this invention is to prosigned to activate a lock-out circuit in the event the armature current exceeds a predetermined value as a result of high counter E. M. F.

In addition to the features above noted as specific objects, the control system of this invention also incorporates the various features heretofore found desirable in hoist motor controls as, for instance, leading all of the motor current through the series brake coil to assure its release, placing the series brake coil outside the dynamic braking loop but always in the circuit to assure positive operation in hoisting and lowering, and the usual low voltage and overload protection.

With the above and other objects in view which will appear as the description proceeds, this invention resides in the novel combination and arrangement of circuits substantially as hereinafter described, and more particularly defined by the appended claims, it being understood that such changes in the precise embodiment of the hereindisclosed invention may be made as come within the scope of the claims.

The accompanying drawings illustrate one complete example of the physical embodiment of the invention constructed in accordance with the best mode so far devised for the practical application of the principles thereof, and in which:

Figure 1 is a diagram of the motor circuit of this invention;

Figure 2 is an across-the-line diagram of the control circuit for opening and closing the switches or contactors of the motor circuit;

Figures 3 to 8, inclusive, show the operative portion of the motor circuit at each of the successive speeds during lowering;

Figures 9 to 14, inclusive, show the operative portion of the motor circuit at each of the successive speeds during hoisting;

Figure l5 illustrates the hoist limit circuit; and

Figures 16 to 21, inclusive, show the operative portion of the control circuit at each of the successive speeds during lowering.

Broadly stated the control system of this invention comprises a motor circuit (Figure 1) which includes a reversible electric motor, a series brake, a resistor bank divisible into sections, contactors or switches and circuit connections made and broken by the closing and opening of the contactors or switches to connect the motor with the current supply through various combinations of resistor sections.

The switches or contactors in the motor circuit are opened and closed by means of a control circuit (Figure 2) which includes a manual master controller, coils to be energized by speed selecting manipulation of the master controller, time delay means for preventing too rapid acceleration of the motor speed and means for precluding operation of the motor at highest speed in the event of heavy hook loads.

To insure high torque for the lifting of heavy loads, the motor used is of the D. C. series type. A lowy torque low speed characteristic desirable for light hookoperation during hoisting is obtained by introducing a shunting resistor across the field and armature. This shunting resistor is removed from the circuit in steps to produce increases in speed in the hoisting direction up to an intermediate point. Beyond this point further increases in speed in the hoisting direction are obtained by shunting out series resistors.

During lowering, dynamic braking is employed to assure control, and to stabilize the speed in lowering the eld is excited by current drawn fromthe line through current limiting resistance while the armature is connected to low voltage points obtained in a novelmanner which'lends itself well tovreuse of resistor sections.

When heavy overhauling loads deliver power back through the gear mechanism to the motor this power is converted into electric energy-which is dissipated in the field and resistor circuit.V At higher speeds, when this energy exceeds the amount that can be so dissipated it is returned to the line.

Adequate toroue at low speed is assured by providing a strong eld, and sinceall of the eld current passes through the winding of the series brake positive release of the brake is assured. The series brake engages automatically in the event of voltage or current failures which might be introduced by the tripping of an overload device, the blowing of a fuse, the opening of a breaker or failure within the power distribution system.

Dynamic braking is maintained at all times in lowering, and through a novel utilization of resistor sections a plurality of dynamic braking loops is provided when lowering at low speeds.

In lowering the speed is increased in three ways, one, by the insertion of resistance into the armature circuit which permits the armature to operate at a higher voltage and consequently higher speed; two, by connecting the armature across points in a potentiometer circuit which will further increase the voltage thereon; and, three, by weakening the iield and thereby requiring a higher speed of the armature to produce a the'proper counter E.

Such weakening of the eld affords a high speed, light hook lowering condition, which usually is atleast two hundred percent of full load speed. The manner in which this high speed, light hook load lowering condition is obtained speeds up operation of the hoist and increases its productive eiort, and at the same time eliminates the attending maintenanceproblems involved in the application of load brakes. In this connection it is important to also point out that by virtue-of a novel'lock-out circuit lowering of heavy hook loads at highest speed is precluded.

Another feature of the invention resides in the fact that the circuit is so arranged as to enhance the control which the operator has over the hook load by spacing the successive speed change points closely at low speed and spreading them out at the higher speeds. This arrangement assuresa, gradual increase at low speeds anda steep or more accelerated increase at higher 4 'd speeds, and as a natural consequence assures smoother operation. This follows from the fact that heavy hook loads have a tendency to spread out the low speed change increments in lowering, and light hook conditions spread out the low speed change increments in hoisting.` Thus, operators can handle light and heavy loads with almost equal dexterity.

The invention also incorporates automatic acceleration control so that the operator cannot produce undesirable results by bringing the controller handle over too rapidly. v

Time delays, however, are not used in deceleration oi the motor since in decelerating (when lowering), the motor not only must absorb the energy delivered back to it by the load through the gear mechanism under a steady state, but it must also provide the necessary torque to decelerate the load when the operator decides to slow down the lowering speed. Time delays at this juncture might take control away from the operator when it is needed most.

1n the drawings, letters have been appended to the reference numerals (where applicable)v to correlate the coils oi the control circuit with the switches, in both circuits, actuated thereby. Thus, the coil designated with the letter An actuates all switches bearing the letter A as a sux.

MOTOR CIRCUIT v Figures 1 and 3 to 8, incl.

The motor circuit comprises the motor having an armature 5 and armatureV and field windings and l respectively, and means for connecting the same across lines LI and` L2 with thecurrent flowing in the armature in one direction for hoisting and in the reverse direction for lowering. Main switches 8 and 9 are connected in the lines LI and L2 and switches I B and I ID are connected between the line LI and the motor to reverse the direction of the current through the armature.

With thesvvitch IBB closed the motor runs in the direction for lowering, and when the switch I ID is closed the motor runs in the reverse direction for hoisting.

A conventional hoist limit switch indicated generally by the numeral I2 is provided to protect the apparatus against the consequences of the operators failure to reverse the controller in time during hoisting. As shown in detail in Figure 15 the actuation of the limit switch disconnects the motor from the line and closes a dynamic braking loop through a resistor I3.

The armature and field windings are connectable with the line L2 through a plurality of resistor sections lli, Eil, I and Il in various seriesparallel combinations depending upon the positions of switches IBF, YIQG, 25E, EIA, and 22C. Two parallel resistor paths are shunted across the armature and eld to provide two independ-- ent dynamic braking loops. One of these paths comprises a resistor ZSand a normally closed may be sections of a suitable grid type resistance, and as will be hereinafter more fully described these same resistors are utilized both during lowering and hoisting. There are, therefore, only six resistors or resistance sections used in the entire motor control circuit and nine switches or contacts, namely, the switches IDB, HD, I8F, IBG, E, 2 IA, 22C, 24H and 25J.

In Figures 3 to 8, inclusive, only the operative portion of the motor circuit at each lof the six speed selecting positions of the master controller is illustrated. Thus, Figure 3 shows the condition of the motor circuit at the first speed during lowering. In this position of the controller, as in all its lowering positions, the switch ISB is closed so that the armature is connected in parallel with the field.

In this first position (Figure 3) a strong field current of between 100 and 200 percent is obtained; the actual current in the iield being dependent upon the hook load since the counter E. M. F. produced by cverhauling loads is fed back to the field through the dynamic braking loops, both of which are closed at this time to connect the armature across the field. The series brake has, of course, been released by the strong current ilowing through its coil 2l; and since the switches I 8F and 20E are closed the resistor sections I4, I5 and I 6 are in the field circuit.

In passing from the first speed in lowering to the second speed (Figure 4) the switch ZEJ is opened thereby removing one of the shunt paths in series with the armature. The opening of this shunt path increases the resistance afforded by the remaining shunt path and has the effect of increasing the voltage across the armature. This allows the armature to increase its speed in response to the hook load to bring the counter E. M. F. into balance with the increased voltage across the armature. For the third speed in lowering (Figure 5) a bridge circuit is established by the closure of switch 22C. The establishment of this bridge circuit further increases the voltage across the armature and thus allows the same to assume a higher speed.

To obtain the fourth lowering speed (Figure 6) the remaining shunt path connecting the armature across the eld is removed by the opening of switch 24H. This leaves the armature connected to the resistor network then in the circuit in such a way as to further increase the voltage in the armature circuit and thereby effect further increase in lowering speed.

Attention is directed to the fact that throughout all these speed changes a closed loop is maintained containing the armature, the field and some resistors so that regenerative power can be dissipated even though voltage failures may be encountered.

To obtain the fifth speed in lowering (Figure 7) switch 20E is opened and switch I9G closed. This transfers the armature to line Voltage. Attention is directed to the fact that the closure of the switch ISG takes place after the switch 20E opens. The reverse order of operation of these two switches would produce considerably higher transient current peaks since it would involve both switches being closed at the same time thereby shorting out much of the resistor network, speciiically the resistor sections I5 and I6, and momentarily drawing heavier current for the eld as well as the armature. The opening of the, switch ZUEbefore closure of the switch ISG 6 permits a resistance transfer which will minimize the current peaks and thereby enhance both commutator life and contactor life.

In the steady state position for the fth speed lowering, the armature is essentially at line voltage and the ield is excited by slightly less than full load current. Only the resistor I'I remains in the armature circuit and this resistor serves to limit the current peaks as the transition is made. As will be hereinafter describedtime delays are employed in the transfers between fourth and fifth and also fifth and sixth speeds.

To obtain the highest or sixth speed in lowering (Figure 8) the field is weakened by connecting the resistor I6 in series therewith. This is done by opening the switch I8F. However, as will be hereinafter more fully described, means are provided to preclude transfer into the sixth or highest speed in lowering in the event of heavy hook loads. The means for effecting this lock-out involves the current responsive relay, the coil 28K of which is at all times connected in the armature circuit. If the hook load is sufficiently light the current responsive relay remains inactive and permits transfer into sixth speed.

In 'returning to lower speeds (still during lowering) fifth speed is obtained by increasing the eld strength by shorting the resistor section I6 out of the eld circuit through the closure of switch I8F which, of course, reduces the speed of the armature.

Fourth speed (Figure 6) is obtained by closing the switch 20E and directly thereafter opening the switch ISG. The field is thus rst strengthened while both switches ISG and 20E are closed, leaving only resistor I4 to limit the eld current. The resulting momentary strong lield tends to increase the counter E. M. F. of the armature and this in turn tends to deliver more current to the resistor network so that when the switch ISG opens, a reduction in current has already started, relieving the load which the switch ISG *must open.

To return to third speed (Figure 5) one of the two shunt circuits across the armature and eld is reestablished by permitting closure of the normally closed switch MH. This reintroduces the bridge circuit.

The second speed lowering (Figure 4) is obtained by opening switch 22C leaving the armature connected through the resistor 23 directly across the eld; and the final reduction in speed in lowering (Figure 3) is obtained by permitting the remaining normally closed switch 26J to reinsert resistor 25 and thus reduce the resistance in the armature circuit by the extra parallel path thus provided.

In the off position (in which position the motor circuit is shown in Figure l) the armature, the eld and the two parallel resistor paths are connected in such a way that any power generated in the motor as a result of hook loads produces a dynamic braking effect. This dynamic braking affords valuable assurance against the acometer switch' .I ID. r Such ireversal zofthef. switches IOB and "I ID; as noted.` hereinbeforadeiects a :reversa-l of current through the. armature .but .leavesthe direction. of` current. through the field .'.thesame as in lowering.. Initial actuation. of the .controller to effect hoisting also closes the switch IBF'whi'ch remains. closed during. alLthe hoisting speeds..

As ywill appear from .a consideration. of Figures. 9 to 14,:inclusive., thesame resistor sections used.

to `provide speed ,control in loweringare'also ern.- ployed to obtain diierent hoisting. speeds.4 Thus, for the first or lowesthoistingspeed .(Fi'gure 9). the resistors 23 andA 25are` connected inparallel across `thearmature and eld. This produces low voltage conditions giving a low speed'. for taking uptheslackinlthe cable.

In secondv speed (Figure l) one of theparallel paths in the shunt is removed to provide. an increaseinlight hook speed for Amanipulating light loads,v this Abeing accomplished` by .the ropening oiA theswitch 24H.

In third'slgieedA (Figure 11) the remaining. para-llelshunt lpath. across the armature andV field-'is removed by the opening of the switch 26.1. This develops a simple-series connection with the -re-4V sistors I4 and I5 in the circuit. l

Fourth, fth and sixth speeds (FiguresrlZ, 13 and 14) are obtained by reducing the amount of resistance-in series with' the motor, rst by Aclosure-of theswitch ZIA to short out the resistor section I4 for fourth speed, next by establishing aparall'el path through resistor section I6 bythe closure of switch 23E, and `in the highest or sixth speedthe switch IQG is closed to short out theresistors I VandIG and connect the armature and ieldof the motor directly across the line.v

As noted hereinbefore, a feature of this `invention residesl in the fact thatthe increment-sof Speed` changeare small at low speeds and larger at high speeds. This is brought about by the way in which the resistor network is arranged and the sections thereof are utilized to develop the. different speeds. For instance, at low speeds the changes in the Voltage impressedupon the armature as the controller is moved from one position tov another are. relatively small because. of the stepwise removal of the two shunt paths containing the resistors 23 and 25, whereas at higher speeds the changes in voltage impressed upon .the armature as .the Vcontroller is moved from. one position to anotherbeing brought about byv the introductionof the bridge circuit with the closure of the VswitchU22C. and the subsequent Vchanges in ser-iesconnected resistance-occur in larger steps. It is, of course, to be understood that'theiohmic valuesoi theA various resistor sections, mustybe chosen with this objective in mind..

THE'` CONTIROL CIRCUIT Figures 2 and 16 to 21, incl.

The control circuit incorporates a master conthe coil ,42' off: an undervoltage protection :relay-is energized-,n the circuittherefor- -passingvthrough the closedilcontactv 39, anydesired, numberof.: emergency stopswitches and closed overloadprofA tection 'switches OLA and OL.2. the coils ofV which are designated by the same charactersxin `the motor'circuitgFigure 1.

With :the energization ofthe .coil-i dr'switches UV; I- and-UV.; are closedthereby connecting-.the linesI LLIandLL2 with the source ofcurrent..

Since the contact 39v is openiin all positions of the controller otherthan its oi. position;v itfol'- lows that; if for any reason-as for instance, opening of one of theemergency stop switches,.open ing of one of the overload switches oit-.insufficient voltage to` coil 4T-the coilV I2'Jbecomesfdeenergized, it is necessary to return the: master controller to its off position to.close itszcontact139.l before the control circuit can be reactivated.` By requiring such reclosure. ofV thecontact'iassurance is automaticallyhad .against starting the motor at anybut lowest speed:

THE. SPEED CHANGES`DIJ`R'IIEDKZ1.A LQWER'ING of thecoilllSB also olosesswitchIfB in the con- 4 troller'provided with contacts 30 to 39, inclusive,

With the master;controllerV in its ofi positrol circuit and switch IIIB, inthe motor circuit to connectthe armature forl operationinthe lowering direction. It is to be notedlth'at. thecoil 43B remains energized` to hOldthe,.-Swtch I 0B closed throughout all; lowering positionspf the controller.

Energization of the coil 44E closes the. switch 20Ein the motor circuit and opens switchAfIEn. the control circuit.

Energization of the coil'45F'closes switch ISE in the motor-circuit and sWitch48F`in thev control circuit.

Thus, withfthej energization of'theucoi'ls 43B, 44E' and 45E, the operative portion offthe; control circuit will be asshown in Figure lianddthisin turn places the'motor circuit-inthe condition v shown in Figure 3.

Moving the master controller to the'rsecond lowering position closesits contactvain'gaddition to those already-closed, toenergizewcoil' 49.1 'and with the energization of coil 49,1 switch 26jV in the motor Avcircuit is opened to cutout onecof the two parallel shunt paths connecting-the arma@- ture across the eld. The operativeportion'of theA control circuit at this junctureis as shown in Figure 17 and "the operative portionof the motor circuit is as shown inliigurel;v

MovingV the` master controller to-- its:4 third lowering position closes its contac-tfy 32` inaddition toA those already closedY andltherebyreiects energization of coil- 50C; The energization ofethe coil 50C closes switch-` ill-2C` inthe motoricirc-uit and closes switch IC in the control circuit. The operative portion of the control circuit at this position of the controller is as shown in Figure 18 While the operative portion of the motor circuit is as shown in Figure 5. Attention is directed to the fact that in thecontrol circuit the closure of the switch 5IC established a path for the energization of the coil 45F parallel to that including the controller contact 35.

Bringing the controller to its fourth speed lowering position closes its contacts 36 and 31 in addition to those already closed. With the closure of contact 31 coil 52H is energized` and its energization opens switch 24H in the motor circuit to cut out the remaining shunt path connectingI the armature across the field. Energization of the coil 52H also closes switch 53H in the control circuit but since the switch 41E in series therewith is open at this time closure of the switch 53H is without effect.

The operative portion of the control circuit in this fourth speed stage is as shown in Figure 19 while the operative portion of the motor circuit is as shown in Figure 6. I

With the energization of coil 52H the time controlled switch 54H begins to open but until it opens the circuit passing through the switches 54H and 4B'B parallels the circuit containing the controller contact 34 to maintain energization of the coil ME even after Opening of the contact 34.

As the controller moves to its fifth lowering speed, its contact 34 is opened but all its other closed contacts remain closed. The opening of contact 34 interrupts one of the two parallel circuits maintaining energization of the coil 44E but as noted above until the time interval for which the switch BAH is set runs out coil ME' remains energized. This time delay affords automatic acceleration control in passing from fourthl to fth'speed.

Of course, if the controller is held in fourth speed for a period longer than the time interval for which switch EMT-T is set. the opening of the contact 3d bv bringing the controller to its fth speed position immediately effects deenergization of the coil 44E. Such deenergization of the coil 44E' opens switch 20E in the motor circuit and permits switch 41E in the control circuit to reclose.

With such reclosure of the switch 41E coil 55G is energized, the circuit therefor passing through contact 3S on the controller and the then closed switch 53H. Energization of the coil 55@ closes switch IBG in the motor circuit and starts the opening of time controlled switch 5iG which is in shunt with switch 481i in the control circuit.

The operative portion of the control circuit at this fifth speed lowering stage is as shown in Figure 20 and the operative portion of the motor circuit is as shown in Figure 7.

Attention is directed to the fact that inasmuch as the reclosure of the switch 47E was necessary to eiliect energization of the coil EEG opening of the switch 20E which takes place with deenergization of the coil 44E had to precede closure of the switch ISG brought about by energization of the coil 55G. This assures against the obiectionable condition of shorting out both resistors I5 and I5 as noted hereinbefore in the description of the motor circuit.

Upon bringing the controller to its highest or sixth speed in lowering its contact 35 is opened. The opening of the contact 3!i has as iis purrose deenergization of the coil 45F but before this coil can be deenergized the parallel holding circuit controlled by switch EGG and a parallel switch 51K must be opened. The switch 56G incorporates a time delayed opening and the switch 51K is controlled by the current responsive relay, the coil 28K of which is at all times connected in the armature circuit. Thus, unless the armature current is below the critical value for which the current responsive relay is set, the coil F will not become deenergized and transfer of the motor circuit to its sixth speed lowering condition shown in Figure 8 is not possible. For the motor circuit to be brought to its sixth speed lowering condition requires opening of the switch ISF, and since switch IBF remains closed as long as coil 45E' is energized it follows that this highest speed cannot be reached as long as a heavy overhauling hook load maintains the armature current in excess of that for which the current responsive relay is set.

The time controlled switch'EG guards against opening of the holding circuit for the coil 45F by transient fluctuations in the armature current which might cause momentary opening of the switch 51K. Y

Since the maintenance of the holding circuit for the coil 45F is dependent upon a condition which may or may not exist this circuit has been shown in dotted lines in Figure 21 which illustrates the operative portion of the control circuit in the steady state sixth speed lowering condition.-

The manner in which return of the master controller through the six lowering speeds and back to its off position effects the functioning of the control circuit and through it the motor circuit can be clearly traced on the drawings.

THE SPEED CHANGES DURING HOISTING The various circuit arrangements which obtain at the different speed changes during hoisting can be readily traced in Figure 2 and hence need no extended description. In all six hoisting speeds the contact 33 of the master controller is closed to energize coil 58D. The energization of coil 58D closes the switch I ID and, of course, since coil 43B is deenergized during all hoisting positions of the controller, the switch IDB in the motor circuit is open and the motor runs in the proper direction for hoisting.

With the energization of the coil 58D the normally closed switch 59D in the control circuit is opened and the normally open switch 60D in parallel therewith is closed.

The contact 35 of the master controller which controls energization of the coil 451i is also closed in all positions during hoisting so that the switch ISF in the motor circuit is closed as long as the controller is in any hoisting position (to the left of off in Figure 2).

In the fourth speed hoisting position of the controller its contact 30 is closed to energize coil 6I A, the mechanism oi which is interlocked with that of coil SB as indicated. With the energization of the coil @lA switch 2IA in the motor circuit is closed and time controlled switch 62A begins to close. The time factor of the switch 62A precludes too rapid acceleration by preventing energization of the coil 44E until switch 62A has timed cut. Normally energization of the coil 44E takes place upon bringing the controller to its fth hoisting speed in which position its contact 34 is closed, it being understood that switch 43B is not closed during hoisting.

y Iwan the -energizauon of .the .noir-44E, Y which Vrequires the controller being in its fifth speed position, -time controlledswitch'ESEin thecontrol circuit begins `to closeand switch-47E is opened. The energization lofcoil 44E also closes switch ZUEin-"thevmotor circuit to place the motor .circu'itf-infthecondition shown-inF-igure 13.

--In theffinallor highest speed of hoistingthe v'factor control built into the switch 63E.

From the foregoing description taken in connection with. the accompanying drawings, it will '-be readily apparent tothose skilled in the art "that this invention provides-a control system for hoist motors which has many advantages over systems heretofore used, p-articularly in regard to reduction in the number of 'switches or contactors required fand the decreasein the-sizeof the refsistorbankwhich resultsfrom the fact that most "lof-fthe"resistor'lsections are 'used and 'reused in bothv lowering and hoisting.

Vlllh'a't claim as my invention is:

' 1. A control system for hoist motors, comprisring: Ya. reversi-ole motor having armature and :eldf windings; a controller having a number of 'ldiierent speed selecting positions for hoisting VYand also for lowering;

a resistor bank; controller-seleo'ted circuit means for connecting seotions of said resistor bank into the armature "andi-field circuits with said sections arranged in different series-parallel combinations at the dif- .ferent speedselecting positions of the controller .'dnring..ilowering; and 'controller-selected circuit flmeans vfor'connecting the same resistor sections .intox the .armature and iield circuits in different `seriesf-lparallel combinations at the diierent l .fspeed selectingpositions of the controller during .Ihoisting' whereby the same resistor sections are iu'sedin/hoisting and lowering.

2.1In.aV motor control. system of the character ldescribed: lia motor. having armature and `field windings; a controller having a plurality of positions; aybank ofiixed resistor sections; cirr-'ciiitme'a-ns governed by the controller for convnectingtheiresistor sections into the armature and field circuits in different series-parallel com- Lbinationsias the controller is moved from one `v:positionitoanother to thereby regulate the motor speed; `a lock-'out circuit .adapted to preclude placing-the resistor'sections in the combination `necessary to effect maximum motor speed; a current responsive relay connected in the armature circuit; fand means responsive to energization fof'said relay for rendering the lock-out circuit foperative sothat operation of the motor at maximumspeedisimpossible if the current owing in the-armature circuit exceeds the critical value of `therelay.

3. v-In-a motor control system for hoists and `"thelike: a motor having 'armature and field windings; a controller having an oi position and aplurality of speed selecting positions for motor speed control vduring hoisting,y and a plu- ;yralityl-of *speed selecting positions for motor .f'spee'dz control duringv lowering;. resistanceV means divisible into sections; .controller-governed cir- Vcuitmeans forconnectin'g/sections of the resist- :ance'lmeans into the armature and eld :circuits Yas '.lth'e controller is moved lto Yits Y.differ-ent positions to bring 'about correspondingspeed regulation Lfor Ith'eamotor; .a lock-out circuit loperable .to'preclude connecting .the resistor sections in the combination required YtOLeect maximum "speed i'in lowering; control instrumentalities operable to render the lock-outLcircuitefective;and means connecting ther control instrumentalities with.: the armature "so lthat v.thefcondition Tof the control .instrumentalities :is :a "reflection iof..,hook .loadand' whereby'the response lof the armature .to heavy hookloads. acting through said control .iinstrumentalitiesactivates the'lock-out circuit.

4.,5A motor control systemfor' hoists, compris` "ing :Y a.. motorhaving iarmature andzeld windings g' a resistor bank; circuit means for connecting sections of nthe resistor 'bankin different combinations into the-armature and fieldcircuits 'to eiect changes in the vspeed-of 'the motor, cer- 'tainof saidcircuitmeans providing'a plurality of independent normally closed dynamic braking loops each including the armature and viield windings, a resistor sectionan'd ya normally'closed switch Hall connected in series whereby said dynamic braking vloops also Aprovide 'a plurality oi parallel shunt'paths connecting'theV armature vacross the -eld winding so that the resistors of *said paths 4constitute a factor"determining the voltage impressed upon the armature; andm'eans Lfor''sequentially fopening said Vn ormally closed switches 'to y'open said shunt paths one at a time and" thereby effect stepwise increase in the volt- '.agepn thearrnature to vbring about stepwise in crease in motor'speed.

5. YVAihoist motor control system, comprising: a

. DFC. series "type motor having armature fand .-nel'd r windings; .a lplurality'of resistors; circuit V'means -for yconnecting the armature :and .eld windings with a source of power with said wind- Viings'inp'arallel and in series with certain of the resistors for'op'eration'of the'motor at speeds-depending upon -thefarrangementand 'number of. the' 'resistors so `connected; anden-cuit `means rconnectinganother of said resistors into a closed loop containing the armature and field windings, lwhereby :said` closed loop yprovides dynamic brakin'giand the'opening thereof increases the voltage impressed upon the armature to eiect an "increase in motor speed.

cr'A hoistrnotor'control system, comprising: a Dj'Crseries type 'motor Vhaving armature and eld windings; a plurality of resistors; variable circuit means 'for Aconnecting the armature 'and field windings `with a power `source with said -wind'ingsin parallel and with certain of the resistors inseries Ywith the armature and field Iwindings for'operation'of the" motor vat speeds Vdepending upon the arrangementand'number of resistors so connected; and` circuit means `for connecting other ci Asaid resistors yinto a number of `parallel closed loops, each containing the armature-fand'field windings Aand a normally closed'svvitchfsaid closed -loops providing a plu- .ralityof dynamic -braking loops and the open- -ingfof -the normally closed switches in said loops increasingthe voltage impressed upon the armatureand thereby increasing the motor speed.

7. The hoistmotor controlfsystem set forth in claim 6 further characterized by .the provision of means for -precluding simultaneous opening of "said normallyclosed rswitchesnso that .the .in-

crease -in voltage impressedupon the Varmature resulting from the opening of said rloops takes 13 place in spaced steps to provide stepwise increase in motor speed.

8. A hoist motor control system, comprising: `a motor having armature and field windings; a resistor network; circuit means for connecting the armature and field windings with a power source through the resistor network with the resistors of the network connected in diierent seriesparallel combinations for diierent motor speeds; means for varying said combinations of the resistor connections and thereby effecting motor speed control; a current responsive relay; circuit means for connecting said relay into the armature circuit; and a lock-out circuit activated by said relay and operable to preclude connection of said resistors into the combination necessary for highest speed so that at heavy over-hauling hook loads when the back E. M. F. provides high armature current transfer into said highest speed is precluded.

9. 'Ihe hoist motor control system set forth in claim 8 further characterized by the fact that the lock-out circuit includes a switch operated by the current responsive relay; and circuit means including a time controlled switch paralleling said relay operated switch for preventing the activation of said lock-out circuit by transient current peaks in the armature circuit.

10. A hoist motor control system, comprising: a motor having armature and eld windings; a resistor network; circuit means for connecting the armature and eld windings with a power source through the resistor network with the resistors thereof connected in different seriesparallel combinations for different motor speeds; a manually operable controller; a control circuit including said controller and operable to vary the arrangement of the resistors in said network to bring about the different motor speeds; and time controlled switches connected in said control circuit and through which pass the circuits necessary for effecting increase in motor speed at certain speed change steps, the timing of said switches delaying change in the connections of said resistors to eiect increase in motor speeds at said speed change steps and thereby providing automatic acceleration control.

11. The control system set forth in claim 10 further characterized by the fact that said time controlled switches are ineiective during reduction of motor speed so that deceleration of the motor is at all times under direct control of the operator.

12. A hoist motor control system, comprising: a motor having armature and field windings; a plurality of resistors; circuit means including switches for connecting the resistors with the armature and field windings in diiierent seriesparallel combinations; and means for opening and closing said switches to select the combinations into which the resistors are connected to enable selection of motor speeds, said combinations being so arranged that at low speeds the increments of speed change brought about by transfer from one combination to another are small while at high speeds said increments of speed change are relatively large.

13. A hoist motor control system, comprising: a D. C. series type motor having armature and held windings; a plurality of resistors; circuit means including switches for connecting the resistors in different series-parallel combinations with the field windings; means for opening and closing the switches to select the combinations into which the resistors are connected to enable selection of motor speeds, certain of said switches if concurrently closed providing a short circuit around more than one of the resistors; and means precluding concurrent closure of said last named switches to thereby guard against undesirable transient current peaks and obviate the interruption of large currents by the opening of said switches.

14. A motor control system including a motor having armature and field windings, a controller and controller-selected circuits for connecting the motor with its power source and controlling its direction and speed, characterized by the provision of circuit means providing a plurality of dynamic braking loops each connecting the armature across the field, and each containing a resistor and a normally closed switch in series therewith, and controller-governed circuits for sequentially opening said normally closed switches to open said dynamic braking loops one at a time.

DORN L. PETI'IT.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,848,563 Santini Mar. 8, 1932 2,078,684 Riley Apr. 27, 1937 

